Leaf litter input from riparian landscapes has been identified as both a major energy flow to stream ecosystems and as a food source for stream macroinvertebrates. In this study the benthic macroinvertebrate community was used to evaluate the decomposition of organic matter in river systems. The aim of this work was to study the decomposition of organic matter using the benthic macroinvertebrate colonization. The research was developed over five months (January 2011 to May 2011) in four different sites, distributed along the River Ferreira terminal area, northern Portugal. A litter bag experiment was used to examine the role of macroinvertebrate communities in the processing of organic material on the river. Litter bags were placed in the water and collected every 7, 15, 30, 60, 90 and 120 days. In litter bags was observed a high abundance of Oligochaeta and Chironomidae, which are characterized by being detritivorous-herbivores and filtering collectors, respectively, indicating the benthic macroinvertebrate more involved on the decomposition of organic matter. These results contributed to increase current knowledge about benthic macroinvertebrate communities and may serve as incentive for future research works.
The dynamics of organic matter is a process which is important for the functioning of aquatic ecosystems, because in addition to the recycling of nutrients, it contributes to the existence of organisms that feed on the same material. In this way, the organic matter in aquatic ecosystems has a fundamental role in many processes, focusing the decomposition [
In the biotic communities, benthic macroinvertebrates have a great importance in aquatic ecosystems, as they play an essential role in the process of organic matter decomposition, especially the allochthonous material [
The amount of leaf material has a great importance in the determination of abundance benthic macroinvertebrates [
In recent years several studies have investigated the decomposition of leaf litter in freshwater systems using leaves contained within litter bags [9,10]. Several studies suggest the use of litter bags in order to study the colonization of macroinvertebrates and how they participate in the degradation of organic matter [11,12]. The high abundance and diversity of macroinvertebrates that colonize the litter bags reinforce the importance of allochthonous plant material [
In this study, we used mixed litter bags, containing leaf material characterized at each sampling site and the main objective is to know which macroinvertebrates participate more in the process of decomposition of leaf material. Mixture of different leaf species were used to imitate natural accumulations in the stream and colonization was compared with that of naturally forming litter bags that were in the stream.
This study was carried out on Ferreira River, situated to the North of Portugal and is in the Douro River basin. The first three sampling sites are located in the municipally of Gondomar and the last sampling sites are situated on the site of the natura 2000 in Valongo. In
This work was carried out an analysis of the plant species representative of each sampling site [
Plastic litter bags were built, with mesh of 10 mm [
In the laboratory the leaf material was identified and stored in a cool and dry place until further use. Immediately before the leaf material was used, it was properly cleaned and placed in an oven at 50˚C for approximately 48 hours.
Within the litter bags were placed 4 g of leaf mixed species. After the leaf material is contained in litter bags, these were closed with string and then were wetted with pure water during transport to the river, to avoid the breakage or loss of the material contained in litter bags.
The litter bags were submerged at four different sites (1, 2, 3 and 4) 12 in each sampling site, and in each litter bag was tied a stone to remain submerged during the entire time of experience and also to avoid losses. The rope used was not bright colors to avoid acts of vandalism [
The collection of litter bags was carried out between January and May (year of 2011), at the following sampling time: 7, 15, 30, 60, 90 and 120 days of exposure of litter bags in the water system. At each sampling site, litter bags were removed for later analysis of samples in the laboratory. At the time of collection of litter bags sometimes used the hand network to help its removal from the river. Each sample was placed into a plastic bag and transported to the laboratory in an icebox.
In the laboratory the leaf material contained in each litter bag was placed in a set of sieves with mesh of 500 and 100 µm and was carefully washed, to remove sediment and other materials without relevance for the experience. Macroinvertebrates were separated, sorted and identified to the lowest taxonomic level as possible, according with Tachet et al. (2003) [
The results were analyzed using the Microsoft Office Excel 2010 and the program CAP 4 (Community analysis package 4; Company PISCES Conservation LDA).
In the statistical analysis it was used only one type of technique in accordance with the existing data and with the objectives that we wanted to achieve that was the Principal Component Analysis (PCA).
Through
Twenty nine taxa were found during the five months of study. A total of 10,738 benthic macroinvertebrates were collected from litter bags.
Through the analysis of
About the taxonomic groups present in litter bags it has been found that the process of succession observed was initiated by the Oligochaeta and Diptera organisms.
Through the analyze of
served a dominance of Diptera in site 1, while in the remaining sampling sites there was a predominance of Oligochaeta. It should be noted that in all sampling sites were present the taxonomic groups Oligochaeta, Diptera and Ephemeroptera. On day 60, in site 1, was not possible to have a collection of their litter bags. In sites 2, 3 and 4, the Oligochaeta organisms were dominant. For the day 90, site 1 has a higher percentage of Oligochaeta and the Diptera were dominant. For the day 120, at the sites 1 and 2, it was not possible to collect the litter bag due to acts of vandalism (the litter bags were polled out of water). In sites 3 and 4 we observed a predominance of Diptera, and low percentage the Oligochaeta, Trichoptera and Ephemeroptera organisms. The scarcicity of Odonata and Trichoptera organisms may indicate difficulty in enters the litter bags because the medium mesh size bags that were used in this study. The author Varga (2001) also found the same situation referred above.
At site 1 were identified a total of 737 macroinvertebrates in the sampling of litter bags (
(95%) at the end of 7 days of immersion and the remaining 5% were filtering collectors (Diptera). At the end of 15 days of immersion, we observed the emergence of mineral scrapers (Gasteropoda) and continued to be present detritivorous herbivores and filtering collectors. On the day 30 appears detritivorous collectors (Ephemeroptera), detritivorous shredders (Diptera, family Tipulidae), mineral scrapers (Diptera, family Dixidae) and continued to persist the detritivorous herbivores, at a lower percentage, and filtering collectors occupying the highest percentage of organisms. At day 90, there was a quite similar situation in relation to the composition of the functional feeding groups for the day 7, with the exception of the appearance of organic scrapers (Diptera, Chirinomidae, Caenidae) and detritivorous collectors (Diptera). During this period study, Oligochaeta was present in highest numbers.
At site 2 we can verify that on 7 and 15 days of exposure of litter bags in Ferreira River, the composition of the functional feeding groups was the same, and there is a predominance of filtering collectors, followed by a lower percentage of detritivorous herbivores, detritivorous collectors and mineral scrapers. At the end of 30 and 60 days after it has been found that the functional feeding groups were similar between the two sampling sites, there is a predominance of detritivorous herbivores, with the emergence of other functional feeding groups. The day 90 it was found that filtering collectors and they was the most abundant.
In site 3 we observed a high percentage of detritivorous herbivores (Oligochaeta) in the days 7, 15, 30 and 60 of immersion. There were a low percentage of collectors filterers in these days, there are also other functional feeding groups in low percentage. At the end of 90 days of immersion, 97% of macroinvertebrates were filtering collectors, 2% of detritivorous herbivores and only 1% of detritivorous collectors. The functional feeding group with higher percentage in 120 days was the filtering collectors (80%), followed by the categories of detritivorous herbivores (17%), detritivorous collectors (2%) and only 1% of organic shredders. It seems that in site 3 there was a similar pattern in the composition of food categories at the end of 7, 15, 30 and 60 days of immersion, as well as the end of 90 and 120 days there is also a high physiologic similarity food.
Comparing
In this study, we identified the nine categories of feeding groups present in litter bags over the time of exposure in Ferreira River, being the filtering collectors present in higher numbers (5986 individuals) following the detritivorous herbivores, with 4346 organisms (Chironomidae and Oligochaeta). These results give us an indication of the organisms that more participated in the process of decomposition of leaf material in real time on the river.
The Principal Components Analysis (PCA) is a method of ordering that transforms the original variables correlated among themselves, in new variables not correlated [
The analysis of
The biggest weight loss observed in the first fifteen days
of colonization is related in part to the leaching of soluble organic compounds in water [
The decrease in total abundance of organisms from 7 to 15 days of immersion may be probably explained due to rainfall, increasing the speed of flow and consequent washing of invertebrates, considerably reducing their number, according Thomazi et al. (2008). Environmental factors contributed to the fluctuations in richness of groups and in density of benthic macroinvertebrates [
As regards the taxonomic groups present in litter bags it has been found that the succession process was initiated by Oligochaeta and Diptera. The Oligochaeta has high variety of food items and when there were leaf accumulations into the aquatic system, there is a higher surface area, promoting the development of microorganisms and consequent abundance [
In this study, we used mixed litter bags [
The colonization makes it possible to get to know the macroinvertebrates presents in the river system, but also enables the analysis of the changes that occur in the composition of the community over time [41,42]. As we observed, litter bags were rapidly colonized by macroinvertebrates, this event is also found by Hieber & Gessner (2002). At site 1 we observe a dominance of detritivorous herbivores and according to the study of Carvalho & Uieda (2004) the Oligochaeta are excellent initials colonizers, hence the high percentage was observed at the end of 7 days. Thus, it has been found that the detritivorous herbivores and filtering collectors remained during all the days of colonization, the Oligochaeta (detritivorous herbivores) are the most abundant. It can be seen that, in site 3 there was a similar pattern in the composition of food categories at the end of 7, 15, 30 and 60 days of immersion, as well in the days 90 and 120 there is also a great physiologic similarity food. In site 4 it was found a balance between detritivorous herbivores and filtering collectors.
These results give us an indication of the organisms that more participated in the process of decomposition, which is Oligochaeta and Chironomidae (Diptera). However, if the study is prolonged in time and if the sampling effort was greater, possibly the results would be more conclusive.